1. Field of the Invention
The present invention relates to devices and methods of water treatment, and in particular to devices and methods of removing organic contaminants from water employing chemical oxidation in continuous flow processes.
2. Description of the Prior Art
Oxidation Technologies have been used in both drinking water treatment and wastewater treatment primarily as a main treatment process to organic contaminates. The use of oxidizers as listed in Table 1 herein, such as for example peroxide is well known, as is the use of UV and Hydroxyl Free Radical Technology. Oxidation is very effective in removal of carbon chains C17 organics and below. The main draw back is the relatively high cost of using these technologies since the dosages of the reactants is significant. However, when employed properly, the results are clean water comprising backbone structures of carbon, nitrogen and water, but without a hazardous waste stream to contend with.
The following table lists several oxidants that may be used in water treatment and their oxidation potential:
TABLE 1OxidantOxidation Potential, VFluorine3.0Hydroxyl radical2.8Ozone2.1Hydrogen peroxide1.8Potassium permanganate1.7Chlorine dioxide1.5Chlorine1.4
As shown in preceding table, hydrogen peroxide is a relatively powerful oxidant. Also shown in the preceding table is the much more powerful hydroxyl radical, a type of free radical, which is second in the list only to fluorine in its oxidation potential. During oxidation processes, especially those involving hydroxyl and/or other free radicals, organic contaminants can be completely or nearly completely mineralized to carbon dioxide, oxygen, water, and a small amount of mineral acids or salts.
For example, hydroxyl radicals can destroy phenols, MTBE, BTEX (benzene-toluene-ethylbenzene-xylenes), pesticides, solvents, plasticizers, chelants, chloroethenes, petroleum hydrocarbons, BOD and COD (biochemical oxygen demand/chemical oxygen demand) contributing compounds, and virtually any other organic requiring treatment. Further, hydroxyl radicals can disinfect process waters and biological effluents, and can decompose amino acids.
Also, hydroxyl radicals can treat water containing chemical warfare agents (e.g., Sarin, Tabun, VX, GF, GX, Cyanide, Soman, mustard gas, etc.); pathogens & biological warfare agents (e.g., bacteria, viruses, anthrax, cryptosporidium, etc.); soil and water contaminants (e.g., MtBE, EtBE, BTEX, chlorinated solvents, DCA, TCA, haloalkanes, methylene chloride, NDMA, carbon tetrachloride, haloalkenes, vinyl chloride, DCE, TCE, PCE, chloroform, acetones, ketones, cyanides, acrylonitriles, phenols, formaldehyde, alcohols, glycol ethers, etc.); ordnance, propellants, and energetic compounds (e.g., TNT, RDX, NDMA, etc.); pharmaceutical residuals (e.g., endocrine disruptors, estrogen, antibiotics, etc.); and/or pesticides (e.g., Dieldrin, Atrazine, IPC, 2,4-D, DDT, etc.), as well as others.
Hydroxyl radicals can be generated during processes involving the catalyzed activation of hydrogen peroxide using such metals as iron, copper, manganese, and/or other transition metal compounds. By far, the most commonly used metal is iron which, when used in the prescribed manner, results in the generation of highly reactive hydroxyl radicals. Iron solutions used as catalysts for this purpose typically include ferrous sulfate, ferric sulfate, ferrous chloride or ferric chloride, and are referred to herein as Fenton's catalysts—named after the chemist who first described the reaction. An example of Fenton-type chemical reaction systems employs ferrous salts and hydrogen peroxide in acidified (pH about 3-6) water suspension, whereby the ferrous ion rapidly reduces hydrogen peroxide to primarily hydroxyl radicals, which can react with and degrade a target contaminant. The peroxide is broken down into a hydroxide ion and a hydroxyl free radical. The hydroxyl free radical is the primary oxidizing species and can be used to oxidize and break apart organic molecules. A further description of Fenton-type reactions is provided in “Fenton's Catalyst—Iron-Catalyzed Hydrogen Peroxide”, which is published by US Peroxide, Laguna Niguel, Calif. and incorporated herein by reference.
The water treatment processes of the prior art use one of several available oxidizers that is added to a volume of water to be treated in a mixing tank at ambient temperature and pressures. Usually the tank is open top and the treatment process has a batch approach to the operation. The dosage of the reactants is high as the mixing energy is low and limited. When hydroxyl free radical is used as the oxidizing agent in the prior art batch processes, it is formed in the volume of water to be treated by adding the reactants into the water so that the reaction takes place in the batch tank, and the large volume of water dampens the effects of the extremely exothermic reaction. A significant drawback to the use of the prior art water treatment processes relying on oxidation technologies, including peroxide and hydroxyl technologies, is the high treatment costs associated with the high dosages of reactants needed to complete the oxidation of the organics to the backbone structure, i.e. the basic elements of carbon, nitrogen and water. In addition, achieving the acidic conditions (pH 3-6) preferred for hydroxyl radical production in the large volumes typical of batch processes can be problematic and highly inefficient.